Method for controlling an internal combustion engine generator unit

ABSTRACT

An actual run-up ramp is measured for internal combustion engine-generator unit during a starting process. The actual run-ramp is then set as the set run-up ramp. In this way, the closed-loop control of the internal combustion engine-generator unit adapts itself to the on-site conditions.

Priority Claim

This is a 35 U.S.C. §371 National Stage of International Application No.PCT/EP2003/012480, filed on Nov. 8, 2003. Priority is claimed on thatapplication and on the following application:

Country: Germany, Application No. 102 52 399.1, Filed: Nov. 12, 2002.

BACKGROUND OF THE INVENTION

The invention concerns a method for the closed-loop control of aninternal combustion engine-generator unit.

An internal combustion engine provided as a generator drive is usuallydelivered by the manufacturer to the end customer without the couplingand generator. The coupling and generator are installed at the endcustomer's facility. To guarantee a constant rated frequency for thecurrent supply into the power supply system, the internal combustionengine is operated in a closed-loop speed control system. In thisregard, the speed of the crankshaft is detected as a controlled valueand compared with a set speed, i.e., the reference input. The resultingcontrol deviation is converted by a speed controller to a correctingvariable for the internal combustion engine, for example, a setinjection quantity.

Since certain data on the coupling characteristics and the moment ofinertia of the generator are often unavailable to the manufacturerbefore the delivery of the internal combustion engine, the electroniccontrol unit is often delivered with a robust set of controllerparameters, the so-called standard set of parameters.

A speed run-up ramp or a run-up ramping rate is stored in this standardset of parameters for the starting process. To allow the fastestpossible run-up, this parameter is set to a large value, e.g., 550revolutions/(minute×second). The previously described closed-loop speedcontrol system and a speed run-up ramp are known, for example, from DE101 22 517 C1 of the present applicant.

In the case of a generator with a large moment of inertia, a largedeviation can develop between the set run-up ramp and the actual run-upramp. This control deviation of the actual speed from the set speedcauses a significant increase in the set injection quantity. In a dieselengine with a common-rail injection system, the significant increase inthe set injection quantity promotes the formation of black smoke. Thesignificant increase in the set injection quantity also causes incorrectcomputation of the injection start and the set rail pressure, since bothof these values are computed from the set injection quantity.

For the manufacturer of the internal combustion engine, the problemsdescribed above mean that for an internal combustion engine-generatorunit with a large moment of inertia, an on-site service technician mustadapt the control parameters of the standard set of parameters to thespecific conditions. This is time-consuming and expensive.

SUMMARY OF THE INVENTION

The goal of the invention is to reduce the adaptation expense for thestarting process of an internal combustion engine-generator unit.

The invention provides that an actual run-up ramp is determined from theactual speed of the internal combustion engine, and the set run-up rampis set to this actual run-up ramp.

A self-adaptive system, which adapts itself to the specific on-siteconditions, is mapped by means of this adaptation of the set run-upramp. This makes further adaptations of the standard set of parametersunnecessary. A significant change in the set injection quantity islikewise suppressed in this way. Therefore, the set injection quantityreaches the steady-state preset value faster. The consequence for therun-up is that the computed injection start and the set rail pressureare in better agreement with the values determined under steady-stateconditions, i.e., certain values are involved. These steady-state valuesare determined by the manufacturer on the test stand and are stored inthe standard set of parameters.

To compute the actual run-up ramp, the speed change in the actual speedis observed within an assigned time interval. The actual run-up ramp canthen be computed, for example, by taking the mean value.

To improve the operational reliability, appropriate limiting values areprovided for the adaptation. Consequently, the adaptation of the setrun-up ramp occurs only when it is within the limiting values.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings show a preferred embodiment of the invention.

FIG. 1 shows a system diagram;

FIG. 2 shows a functional block diagram;

FIGS. 3A, B, C show a time diagram of a starting process;

FIG. 4 shows a characteristic curve; and

FIG. 5 shows a program flowchart.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a system diagram of the overall system of an internalcombustion engine-generator unit 1, which consists of an internalcombustion engine 2 with a generator 4. The internal combustion engine 2drives the generator 4 via a shaft with a transmission element 3. Inpractice, the transmission element 3 can comprise a coupling. In theillustrated internal combustion engine 2, the fuel is injected by acommon-rail injection system. This injection system comprises thefollowing components: pumps 7 with a suction throttle for conveying thefuel from a fuel tank 6; a rail 8 for storing the fuel; and injectors 10for injecting the fuel from the rail 8 into the combustion chambers ofthe internal combustion engine 2.

The operation of the internal combustion engine 2 is automaticallycontrolled by an electronic control unit (EDC) 5. The electronic controlunit 5 contains the usual components of a microcomputer system, forexample, a microprocessor, interface adapters, buffers, and memorycomponents (EEPROM, RAM). The relevant operating characteristics for theoperation of the internal combustion engine 2 are applied in the memorycomponents in input-output maps/characteristic curves. The electroniccontrol unit 5 uses these to compute the output variables from the inputvariables. FIG. 1 shows the following input variables as examples: arail pressure pCR, which is measured by means of a rail pressure sensor9; an actual speed signal nM(IST) of the internal combustion engine 2;an input variable E; and a signal START for the start set-pointassignment. The start input assignment is activated by the operator.Examples of input variables E are the charge air pressure of aturbocharger and the temperatures of the coolant/lubricant and the fuel.

As output variables of the electronic control unit 5, FIG. 1 shows asignal ADV for controlling the pumps 7 with a suction throttle and anoutput variable A. The set rail pressure pCR(SW) is determined by meansof the signal ADV. The output variable A is representative of the othercontrol signals for automatically controlling the internal combustionengine 2, for example, the injection start SB and the injection time SD.

FIG. 2 shows a functional block diagram for computing the injectionstart SB, the set rail pressure pCR(SW), and the injection time SD. Aspeed controller 11 computes a set injection quantity QSW1 from theactual speed nM(IST) of the internal combustion engine and the set speednM(SW). This computed value is limited to a maximum value by a limiter12. The output quantity, which corresponds to the set injection quantityQSW, is the input variable of the input-output maps 13 to 15. Theinjection start SB is computed as a function of the set injectionquantity QSW and the actual speed nM(IST) by the input-output map 13.The set rail pressure pCR(SW) is computed as a function of the setinjection quantity QSW and the actual speed nM(IST) by the input-outputmap 14. The injection time SD is determined as a function of the setinjection quantity QSW and the rail pressure pCR by the input-output map15.

It is apparent from the functional block diagram that a large controldeviation leads to a significant increase in the set injection quantityQSW1. This significant increase is limited to a maximum value by thelimiter 12. This maximum value of the set injection quantity in turncauses a false injection start SB and a false set rail pressure, i.e.,the injection pressure, to be computed.

FIG. 3 has three parts 3A to 3C, which show, in each case, as a functionof time: the behavior of the set speed and the actual speed in theinitial state (FIG. 3A); the behavior of the set speed and actual speedafter the adaptation (FIG. 3B); and the behavior of the set injectionquantity QSW (FIG. 3C). In FIG. 3C, the set injection curve with thesolid line, which is the curve containing the points A to D, correspondsto the initial state. The dot-dash line, which is the curve containingthe points A, E, and D, corresponds to the curve after the adaptation.

First, the process sequence in the initial state will be explained. Inthe initial state, the internal combustion engine-generator unit 1 isoperated according to the standard set of parameters. The discussionwhich follows is based on a generator with a large moment of inertia. Attime zero, the start is initiated. The set speed nM(SW) is set at afirst value nST, for example, 650 rpm. A set injection quantity QSW,value QST, is preset by the speed controller. The actual speed nM(IST)approaches the set speed nM(SW) until time t1 (see FIG. 3A). From timet1 to time t2, a set run-up ramp HLR(SW) is preset by the electroniccontrol unit. A typical value for the rate of increase of the set run-upramp is 550 revolutions/(minute×second). Due to the large moment ofinertia of the generator, the actual speed nM(IST) does not follow theset run-up ramp HLR(SW). This control deviation is used by the speedcontroller to compute a higher set injection quantity QSW, i.e., thecurve of the set injection quantity QSW in FIG. 3 varies from point Atowards point B. The increasing control deviation causes a significantincrease in the set injection quantity QSW. This set injection quantityis set at a maximum value by a limiter. In FIG. 3, this limitation isrepresented as a dot-dash line that runs parallel to the x-axis. Themaximum value is denoted here as QDBR. Accordingly, the set injectionquantity QSW is limited to the value QDBR at point B.

At time t3, the actual speed nM(IST) reaches an idling speed, forexample, 1,500 rpm. This speed value is denoted in FIG. 3A as nLL. Theactual speed nM(IST) subsequently overshoots the idling speed nLL andfinally settles back to this level. Since a control deviation ofpractically zero is now present, the speed controller computes asteady-state value of the set injection quantity. This is represented inFIG. 3C by the value QLL. Consequently, in the interval t3 to t4, theset injection quantity QSW falls from the limiting value of point C tothe steady-state value of point D.

The invention now provides that the actual run-up ramp HLR(IST) isdetermined from the actual speed nM(IST). For this purpose, the speedchanges of the actual speed nM(IST) are observed within an assigned timeinterval. In FIG. 3A, two pairs of values are shown as examples. A firstpair of values consists of the time interval dt(1) and the change inspeed dn(1). The second pair of values consists of the time intervaldt(i) and the change in speed dn(i). The actual run-up ramp can becomputed from these pairs of values, for example, by taking the meanvalues:HLR(IST)=SUM(dn(i))/SUM(dt(i))where

-   -   HLR(IST)=actual run-up ramp    -   SUM=sum in the observed interval (i=1 to i=n)    -   dn(i)=change in speed    -   dt(i)=time interval

After the actual run-up ramp HLR(IST) has been computed, the set run-upramp HLR(SW) is set to the values of the actual run-up ramp HLR(IST).

FIG. 3B shows the adapted set run-up ramp HLR(SW) of FIG. 3A. It isapparent that the set run-up ramp was adapted in such a way that the setspeed nM(SW) and the actual speed nM(IST) are almost identical duringthe time interval t1 to t3. For the computation of the set injectionquantity QSW, this means that, starting at time t1, the set injectionquantity QSW is guided to the steady-state value, here QLL, along thedot-dash line, i.e., along the curve that contains the points A, E, andD.

After adaptation of the set run-up ramp HLR(SW), a smaller set injectionquantity QSW is thus obtained during the engine start, which results inthe avoidance of black smoke formation. At the same time, theinput-output maps in FIG. 2 are computed with a smaller set injectionquantity [[QDW]] QSW. This leads to more favorable operating values.This improves the accelerating power of the engine. Due to thisimprovement, in practice, the set run-up ramp HLR(SW) can be set by agreater run-up ramp HLR(JST) than that determined from the actual speedbehavior. Consequently, the following applies:HLR(SW)=(SUM(dn(i))/SUM(dt(i))+K)where

-   -   HLR(SW)=set run-up ramp    -   SUM=sum in the observed interval (i=1 to i=n)    -   dn(i)=change in speed    -   dt(i)=time interval    -   K=constant (K>0)

FIG. 4 shows a characteristic curve. It shows several set run-up rampsas a function of time. HLR1 denotes the set run-up ramp in the initialstate, as it is mapped in the standard set of parameters when theinternal combustion engine is delivered. In accordance with theinvention, the set run-up ramp HLR1 is adapted as a function of theactual run-up ramp computed from the actual speed nM(IST). In FIG. 4,two additional run-up ramps HLR2 and HLR3 are plotted as examples. Theset run-up ramp HLR3 will occur in an internal combustionengine-generator unit with a large moment of inertia. The set run-upramp HLR2 will occur in an internal combustion engine-generator unitwith a very small moment of inertia. In addition, a first limiting valueGW1 and a second limiting value GW2 for error protection are plotted.Consequently, the adaptation of the set run-up ramp occurs only when thenew set run-up ramp lies within a tolerance band TB, which is defined bythe first limiting value GW1 and the second limiting value GW2.

FIG. 5 shows a program flowchart. At S1, the set run-up ramp HLR(SW) isread in. At S2, a check is then made to determine whether the actualspeed nM(IST) is greater than the start speed nST, for example, 650 rpm.If this is not the case, the program flows to a wait loop at S3. If theinterrogation at S2 is positive, the actual run-up ramp HLR(IST) isdetermined at S4 from the behavior of the actual speed nM(IST). At S5, acheck is then made to determine whether the actual speed nM(IST) hasreached an idling speed nLL, for example, 1,500 rpm. If the idling speednLL has not yet been reached, the program flowchart returns to step S4.

If the actual speed nM(IST) has reached the idling speed nLL, a check ismade at S6 to determine whether the determined actual run-up rampHLR(IST) is within the tolerance band TB. If this is the case, then atS7 the set run-up ramp HLR(SW) is set to the values of the actual run-upramp HLR(IST). Alternatively, provision can be made to set the setrun-up ramp HLR(SW) to the sum of the actual run-up ramp HLR(IST) and aconstant. The program then jumps to program point A.

If the measured actual run-up ramp HLR(IST) is outside the toleranceband TB, then at S8 an error mode FM is set, and the program jumps toprogram point A.

Although the present invention has been described in relation toparticular embodiments thereof, many other variations and modificationsand other uses will become apparent to those skilled in the art. It ispreferred, therefore, that the present invention be limited not by thespecific disclosure herein, but only by the appended claims.

1. A method for closed-loop speed control of an internal combustionengine-generator unit during a starting process, comprising the stepsof: presetting a set speed (nM(SW)) by means of a set run-up ramp(HLR(SW)); computing a control deviation from the set speed (nM(SW)) andan actual speed (nM(IST)); determining a set injection quantity (QSW)for controlling the actual speed (nM(IST)) from the control deviation bymeans of a speed controller; and, determining an actual run-up ramp(HLR(IST)) from the actual speed (nM(IST)), ((HLR(IST))=f(nM(IST))), andsetting this as the set run-up ramp (HLR(SW)).
 2. The method forclosed-loop speed control in accordance with claim 1, including settingthe actual run-up ramp (HLR(IST)) as the set run-up ramp (HLR(SW)) atleast when an idling speed (nLL) has been reached.
 3. The method forclosed-loop speed control in accordance with claim 1, further includingchecking to determine whether the actual run-up ramp (HLR(IST)) iswithin a tolerance band (TB).
 4. The method for closed-loop speedcontrol in accordance with claim 3, including setting an error mode (FM)if the actual run-up ramp (HLR(IST)) is outside the tolerance band (TB).5. The method for closed-loop speed control in accordance with claim 1,including determining the actual run-up ramp (HLR(IST)) from a change inspeed (dn(i), i=1, . . . , n) of the actual speed (nM(IST)) within anassigned time interval (dt(i)).
 6. The method for closed-loop speedcontrol in accordance with claim 5, including computing the actualrun-up ramp (HLR(IST)) from the change in speed (dn(i)) during the timeinterval (dt(i)) by taking the mean value.
 7. The method for closed-loopspeed control in accordance with claim 6, wherein the actual run-up ramp(HLR(IST)) and a constant (K) are added (HLR(SW)=HLR(IST)+K).